the-collector 0.5.1

A library to store robot data in a json file

The Collector

This is still under heavy development

The idea behind this a container that can store data and time tag the data when it is captured. The main structure is a dict which has keys for each data series stored.

This was written for a class I taught on robotics. It is meant to be simple and teach the students some things.

Setup

Install

The suggested way to install this is via the pip command as follows:

pip install the_collector

If you want to do something with numpy or simplejson, then use:

pip install the_collector[numpy]
pip install the_collector[simplejson]
pip install the_collector[all]

The all option installs all optional libraries.

Development

To submit git pulls, clone the repository and set it up as follows:

git clone https://github.com/MomsFriendlyRobotCompany/the-collector
cd the-collector
pip install -e .

New msgpack Version

• You get out exactly what you put it
  • no default timestamp applied to data
• because msgpack does a great job of turning python data into efficient binary data, there is no need for an extra compression step
• OpenCV is not required
• numpy is optional, but if you need it, then a simple pip command will install it (unlike opencv)

from __future__ import print_function
from the_collector.bagit import BagReader, BagWriter


d = {'a': 1, 'b': 2}
bag = BagWriter()

# grab some data
for _ in range(100):
    bag.push(d)

# save it to a file
bag.write('bob.bag')  # .bag is automagically appended if not present

# now read it back
bag = BagReader()
data = bag.read('bob.bag')

Custom Pack/Unpack

You can pass functions to pack or unpack custom data structures to BagReader(pack=...) and BagWriter(unpack=...) as expained in the msgpack docs here

def ext_unpack(msg):
    # do some cool stuff here
    # see msgpack docs for examples

# calls the function ext_unpack when something custom is encountered
bag = BagReader(unpack=ext_unpack)

def ext_pack(msg):
    # do some cool stuff here
    # see msgpack docs for examples

# calls the function ext_unpack when something custom is encountered
bag = BagWriter(pack=ext_pack)

Todo

• I might add back in optional timestamping of data
• I would like to figure out a way to stream data to disk so you don't have to hold everything in memory first

Old Json Version

The old version always returned a dict and always appended a timestamp.

Usage

In the code example below, sensor data is saved to a file. Specifically, it is saving:

• imu: accel, gyro, magnetometer
• camera: raspberry pi images.

Every time data is pushed into the Bag file, each data point is given a time stamp. Thus, for the camera, the Bag (which is a dictionary) would have an array of:

bag['camera'] = [[frame0, stamp], [frame1, stamp], ... ]
bag['imu'] = [[imu0, stamp], [imu1, stamp], ... ]

where stamp is a time stamp, frame is an image from from a camera, and imu is an array of [accel, gyro, magnetometer] data. Now to save data to disk:

from the_collector.bagit import BagJsonWriter
import time

# this file name gives a time/date when it was created
# you don't have to do this, 'data.json' would work fine too
filename = 'robot-{}.json'.format(time.ctime().replace(' ', '-'))

# create the writer
bag = BagJsonWriter()
bag.open(filename, ['imu', 'camera'])

# camera images are binary arrays, we are going to base64 encode them
# so we can store them in a json file nicely
bag.stringify('camera')  # this can be a string or an array of keys

try:
    while True:
        # read and get imu data, say: data = imu.read()
        # always push (key, data), push will add a timestamp
        bag.push('imu', data)

        # read camera, say: ret, frame = camera.read()
        bag.push('camera', frame)

except KeyboardError:
    bag.write()  # actually writes the data to disk

To read data from a bag file:

from the_collector.bagit import BagJsonReader

reader = BagJsonReader()
data = reader.load('my_file.json')  # read in the file and conver to dict

# now print everything out
for key, value in data.items():
    print('-- {} -----------------'.format(key))
    for sample in value:
        point, timestamp = sample
        print(timestamp, point)
    print('')

Compression

You can turn on or off compress to reduce file size. If you use the compression, then it really isn't a json file anymore. Thus, other programs won't be able to read it.

bag = BagJsonWriter()           # or BagReader()
bag.use_compression = True  # or False (default)

Change Log

Date	Version	Notes
2018-07-09	0.5.0	moved away from json and now using msgpack
2017-11-23	0.4.0	fixes, documentation, unit tests
2017-10-04	0.0.1	init

The MIT License (MIT)

Copyright (c) 2017 Kevin J. Walchko

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.